Final answer:
Using strong passwords is the key action to prevent unauthorized access to patient and financial records, complemented by antivirus software installations and regular data backups.
Step-by-step explanation:
The action that prevents unauthorized computer access to any patient records and/or office financial records is using strong passwords. This fundamental security measure ensures that only authorized individuals can gain access to sensitive data. Passwords and PINs should be complex, utilizing a mix of letters, numbers, and special characters, and should not be easily guessed. It is also important to change passwords regularly to enhance security further. Moreover, for comprehensive security, it is crucial to complement strong passwords with additional measures such as installing antivirus software to protect against malware and regularly conducting data backups to safeguard against data loss.